@Kitsu the whole game is already simple, and in my opinion people want to make it banal. Let's say, you have a high level shiny Eevee. One day you decide to make it Vaporeon, another day you want it de-evolve to be Eevee, and pick another evo depending on your... mood. Then it's enough to have one shiny Eevee, you can have all of its evolution now - how comfy
Personally, I think the idea may be good, but not for all of the pokemon. As I wrote above, pokemon with evo via level up or migrated ones can be evolved by accident - and that's okay to use the item in that case. But using it on item-evolving pokemon would be too much, as you can't evolve pokemon of that kind by accident - you do it consciously.
Besides, it will mess up the official stats - between basic form shinies and their evolution stages.
I'm really surprised I'm the only one who can see it.